I think we can all agree that hiring Rex was a mistake, but in the long run, it led to McD being our HC. (I don't think he was a candidate when they hired Rex.)
When Rex was fired, a lot of people said that he set the franchise back 5 years. At the time that seemed true, but in retrospect, I'm becoming more convinced that the Bills are in a better position now than they would have been with any of the other coaches who were available back then.